chore(ci): build PR images as pr-N (#1026)

- Remove event validity check (unneeded and was buggy)
- Remove `branch` metadata trigger since it conflicts with the PR trigger

.github/workflows/ci.yml

@@ -39,21 +39,6 @@ jobs:
     env:
       DOCKER_BUILDKIT: "1"
     steps:
-      - name: Check for event validity
-        if: |
-          !((
-            github.event_name == 'push'
-          ) || (
-            github.event_name == 'release'
-          ) ||  (
-            github.event.pull_request.head.repo.full_name != github.repository
-          ) ||(
-            github.actor == 'dependabot[bot]' &&
-            github.event_name == 'pull_request' &&
-            github.event.pull_request.head.repo.full_name == github.repository
-          ))
-        run: echo "Not a valid event!" && exit 1
-
       - uses: actions/checkout@v3
 
       - uses: reviewdog/action-misspell@v1
@@ -119,7 +104,6 @@ jobs:
             qmcgaw/gluetun
             qmcgaw/private-internet-access
           tags: |
-            type=ref,event=branch,enable=${{ github.ref != format('refs/heads/{0}', github.event.repository.default_branch) }}
             type=ref,event=pr
             type=semver,pattern=v{{major}}.{{minor}}.{{patch}}
             type=semver,pattern=v{{major}}.{{minor}}